Chromium chains as polydentate fluoride ligands for actinides and group IV metals

Abstract

The reactions of {Cr₆} horseshoe chains {[ⁿPr₂NH₂]₃[Cr₆F₁₁(O₂C^tBu)₁₀]}₂, 1 and precursors of actinides and group IV metals led to a series of ring complexes [ⁿPr₂NH₂][Cr₇TiF₆O₂(O₂C^tBu)₁₆], 2, [ⁿPr₂NH₂][Cr₆Ti₂F₅O₃(O₂C^tBu)₁₆], 3, [Cr₆ThF₇(O₂C^tBu)₁₅ (Me₂SO)], 4, [(ⁿPr₂NH₂)₂(Cr₆Th₂F₁₂(O₂C^tBu)₁₆)], 5 and [ⁿPr₂NH₂][Cr₆U₂O₂F₈(O₂C^tBu)₁₆(Me₂SO)], 6. X-ray structure studies indicate that the {Cr₆} chains maintain their structures in these complexes, acting as polydentate fluoride ligands. Their static magnetic properties were measured and fitted by isotropic exchange Hamiltonian. In accordance with 1, the magnetic exchanges between Cr^III are antiferromagnetic, while the exchange interactions can be modified by the tetravalent metals. For compound 6, ferromagnetic exchanges J_Cr–U and J_U–U are obtained. EPR spectra of compounds 2–5 were measured at Q band and were simulated. The spectrum of 2 has the same profile as {Cr₇Cd} and {Cr₇Zn} rings with a ground state S = 3/2. 3, 4 and 5 give similar EPR spectra with S = 0 ground states.